In the description below, the word "switch" is used to denote "switching system" and the nouns "table" and "form" are used to denote "data bits stored in a memory, configured so that they may be read as a table".
A normal stand-alone switch normally has station apparatus such as telephone sets and trunks connected to it, and functions to respond to digits or data received from the telephone sets or trunks to interconnect the telephone sets or trunks to specific telephone sets or incoming trunks to outgoing trunks, when used as a tandem switch. If there is a need for a remote switch to locally interconnect a group of telephone sets, in order to allow communication with the external telephone network, the remote switch is connected to a host switch by means of dedicated trunks which can have direct connections to trunks in the external network through the host switch when the subscriber connected to the remote switch dials a specific prefix number. The numbers dialed by the subscriber connected to the remote switch are therefore not the same as those dialed by a subscriber connected to the host switch, for outgoing calls. The remote switches are thus specialized and have a different design than the host, requiring the telephone company to purchase and maintain switches of different design, which is costly.